The objective of this proposal is to explore the evolutionary mechanisms to how organisms evolve to anticipate periodic changes in their environment. The circadian clock has evolved to anticipate the light/dark cycles of the 24-hour day, and serves as a ideal model for investigating how organisms have adapted to oscillations in their environment. Clocks coordinate the physiology of many organisms with the most beneficial time of day, and disruption of this process in mammals has been linked to depression, insomnia, coronary heart attacks, and cancer. Despite the broad role of clocks in coordinating function with time, the mechanism or benefit to evolving clocks is not well understood. Using the budding yeast, Saccharomyces cerevisiae, this proposal seeks to analyze the evolution of clocks with the following aims: (1) Engineer and improved an oscillating circuit by manipulating an endogenous signaling pathway, (2) Evolved a stochastic switch into a regular oscillator, and (3) Evolve a circadian clock de novo by random mutation and selection. These aims will utilize both conventional genetic and molecular biology approaches to engineer and characterize signaling pathways for all aims. An experimental evolution approach using fluorescence activated cell sorting (FACS) to select for evolved phenotypes will be used for aims 2 and 3. The aims are designed to investigate both the narrow biochemical detail of oscillating circuits that give rise to clocks, and the broad changes to an organism has it evolves an internal clock. Yeast will be used because they lack a detectable endogenous clock, which permits the evolution of one de novo, and genetic changes are much easier to track in yeast than in higher eukaryotes. More generally, this proposal seeks to address the general evolutionary principles to how new biochemical functions arise by natural selection. There is a significant lack of experimental evidence detailing the biochemical nature of the relationship between orgnanism and environment, and illuminating general mechanisms will provide beneficial insight to health issues such as antibiotic-resistent bacteria, cancer progression, and the onset of epidemic outbreaks. The human body has adapted to sense cyclical changes in the environment by virtue of a circadian clock, but the overall biological contribution to this sensing mechanisms is not well understood. Data suggests that disruption of the clock is linked to various diseases such as depression, heart disease, and cancer. This proposal is outlined to explore and determine how organisms develop the ability to sense periodic changes in their environment, and its overall contribution to maintaining health.